The proposed work concerns the oxygenation of the mammalian retina and optic nerve head, and the metabolism of photoreceptors with regard to their oxygen utilization and effect on extracellular potassium. The aims of individual components of the project are 1) to investigate the processes responsible for the high oxygen consumption of the photoreceptors, 2) to develop a mathematical model linking oxygen measurements with metabolic changes, 3) to study the oxygenation of the fovea in a primate, 4) to study the oxygenation of the optic nerve head under conditions of normal and elevated intraocular pressures, and 5) to study the effects of carbon dioxide on retinal oxygenation. Changes in the oxygen supply to the retina are implicated in many retinal diseases, and an understanding of normal retinal oxygenation may provide insight into mechanisms and therapies for these diseases. In particular, measurements of foveal oxygen distribution in the primate may yield information relevant to the question of whether metabolic differences make the human fovea more susceptible to degenerative changes than other retinal regions. Also, the mechanism of glaucomatous damage to the optic nerve is controversial, and the techniques used here can complement other types of studies on this important question. Microelectrodes will be used to record oxygen tension, potassium concentration and electrical activity of the intact eye of anesthetized cats and monkeys. Independent variables to be studied include the state of light adaptation, blood gases and intraocular pressure. Data will be subjected to mathematical analysis to enhance our understanding of oxygen utilization.